50 CIRCULAR 3 3 3, U.S. DEPARTMENT OF AGRICULTURE 



the same age and species grown under favorable conditions. Since a 

 definite standard is lacking, classification as to thrift or vigor is 

 often open to question, particularly if made by different workers at 

 different reexaminations. 



STEM AND CROWN MAPS 



A map locating all trees on a sample plot is called a stem map. 

 Such a map may make it unnecessary that all trees be individually 

 tagged or numbered in the field. In addition to presenting a pic- 

 ture of tree distribution and providing an index to the tree numbers 

 on the plot, it facilitates analytical study; division, for statistical 

 study, of a plot on which all tree data were originally lumped; and 

 elimination of any parts of the plot that develop abnormalities. One 

 or another of these uses will in a great many instances justify mak- 

 ing a stem map. As an index to tree numbers, alone, the stem map 

 may save many hours of work, which in its absence would be con- 

 sumed in relocating irregularly placed numbers and identifying 

 trees that have lost their numbers. It should be remembered, how- 

 ever, that the preparation of a stem map is itself a time-consuming 

 task. The decision to prepare one in connection with a given study 

 should be based on a careful consideration of use and need. 



The field work involved in mapping tree locations is simplified 

 by dividing the plot into squares with string (p. 16). The coordi- 

 nates of each tree in each square can quickly be read with a measur- 

 ing stick 24 and plotted on cross-section paper. If a chain is 

 stretched through the middle of each square the distance along it 

 may be read directly, and the distance to the right or left of it 

 measured with the stick. It is essential in such work that the chain 

 be kept taut, that allowance be made for slope, and that the measur- 

 ing stick be held at right angles to the chain. In open stands, dis- 

 tances within a given strip may readily be determined by the use 

 of a range finder. Tree locations may be mapped with a traverse 

 board or with a plane table and an alidade. Under some circum- 

 stances, when the plot is carefully sectionized, plane table and ali- 

 dade may be dispensed with and a piece of cross-section paper 

 mounted on any fairly smooth, hard surface can be used with a high 

 degree of accuracy. The distances may be measured with a chain, 

 with a range finder, or with a telescopic alidade and stadia rod. 

 If much brush or undergrowth is present, it is impracticable to use 

 the range finder or stadia rod. 



Tree locations can be determined also by the use of the angle 

 mirror (65). Tapes are stretched along the plot subdivisions (right 

 angles are necessary). One man plots the trees while each of two 

 other men walks along a tape holding an angle mirror from which 

 is suspended a plumb bob. As soon as the proper tree is located the 

 coordinates are called to the mapper, who plots the tree's position. 

 Where there is much undergrowth such use of the angle mirror is 

 impracticable, as the plumb-bob lines are frequently caught. Else- 



34 A measuring stick used in dense brush by the Forest Service is a rod marked 

 off in feet and painted in bright colors like a surveyor's sight rod but with the difference 

 that 5 instead of only 2 colors are used, each 5 feet of rod displaying the same sequence 

 of white, orange, blue, yellow, and red. When this measuring stick is used, instead of 

 having to look for numbers or letters to identify the foot distance the cartographer has 

 only to distinguish the identifying color of the foot in question, and this he can do 

 if only an inch of the color shows through the tangle of vegetation. 



